add cups to lp group

We want cupsd to be able to access USB printers, which will have
group:lp.

CQ-DEPEND=CL:350850,CL:*264046
BUG=chromium:616866
TEST=security_AccountsBaseline on trybot
TEST=print to USB printer with non-root cupsd

Change-Id: I8d1d6988cfbe52572f4be89046c86a21c855d880
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/350771
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
diff --git a/profiles/base/accounts/group/lp b/profiles/base/accounts/group/lp
index b9e64c7..634078b 100644
--- a/profiles/base/accounts/group/lp
+++ b/profiles/base/accounts/group/lp
@@ -1,3 +1,3 @@
 group:lp
 gid:7
-users:lp
+users:lp,cups